Foreign object damage resistant vane assembly

ABSTRACT

A vane assembly for a gas turbine engine including a shroud with openings defined therein about a circumference thereof and vanes extending radially from the shroud with a vane tip in each opening. Isolating means are disposed in each opening to isolate the vane tip from the shroud ring. Each vane tip is engaged with the shroud by retaining means for restricting movement of the vane tip in an axial direction relative to said shroud.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 11/223,129,filed on Sep. 12, 2005, the specification of which is incorporatedherein by reference.

TECHNICAL FIELD

The invention relates generally to gas turbine engines, and particularlyto improved vanes provided therein downstream of the engine fan or lowpressure compressor.

BACKGROUND OF THE ART

Gas turbine engine vane assemblies are usually provided downstream ofthe engine fan and/or of a low pressure compressor to reduce the swirlin the air flow exiting the compressor. Such vane assemblies must beresistant to foreign object damage while having a minimum weight.

It is known to provide an inner shroud with slots receiving the vanetips in order to retain them. In such a configuration, a grommet isinserted in the slot such as to surround the vane tip thereby isolatingthe vane tip from the shroud. However, during a foreign object damageevent a vane which is hit will move rearward as a result of the impact,and the vane edge, which tends to be sharp, can cause cutting of thegrommet and damage to other surrounding components. Also, the airflowsurrounding the grommets often produces a force which tends to lift anddisplace the grommets, thus requiring the use of adhesive or othersimilar measures to ensure that they stay in place. Such a use ofadhesive complicates the installation and replacement of vanes.Moreover, the protruding grommets can disturb the airflow, which canalter the engine's performance.

Accordingly, there is a need to provide an improved vane assembly.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide an improved vaneassembly.

In one aspect, the present invention provides a vane assemblycomprising: a shroud including an annular shroud ring and a shroud webradially extending from one side thereof, the shroud ring including aplurality of openings defined therethrough about a circumference thereofin alignment with said shroud web such that the shroud web extendsacross the openings; a grommet located in each of the plurality ofopenings having a cutout therein; and a plurality of vanes supported byand extending radially from the shroud ring opposite of the shroud web,each one of the plurality of vanes having a vane extremity located inthe cutout one of the grommets, the vane extremity having a slot definedtherein which receives a portion of the shroud for mating therewith.

In another aspect, the present invention provides a vane assembly for agas turbine engine, the vane assembly comprising: a vane shroud having ashroud ring portion including a plurality of openings definedtherethrough about a circumference thereof, a web portion extendingradially from the shroud ring portion across the plurality of openings;a plurality of vanes extending radially from a side of the shroud ringportion opposite the web portion, each of said vanes having a vane tipreceived within one of the openings; means for isolating said vane tipfrom said shroud ring portion being disposed in each of the openings;and each of said vane tips being engaged with said vane shroud byretaining means for restricting movement of the vane tip in an axialdirection relative to said vane shroud.

In another aspect, the present invention provides a method for attachinga vane tip in a vane assembly of a gas turbine engine, the methodcomprising the steps of: forming a shroud ring having a plurality ofopenings distributed about a circumference thereof and a web extendingradially from the shroud ring across the plurality of openings;installing a grommet in each of the plurality of openings, such that acutout extending therethrough is aligned with the openings; providing aplurality of vanes, each having a radially extending slot defined in avane tip thereof; and inserting each vane tip into said cutouts of thegrommets within said opening of the shroud ring so that the web isreceived within each radially extending slot.

There is also provided, in accordance with another aspect of the presentinvention, a vane for a vane assembly of a gas turbine engine, the vaneassembly including a plurality of said vanes mounted to a supportingshroud via intermediate grommets, each said vane comprising an airfoilextending radially from a root portion to an opposed tip and defining aleading edge and a trailing edge corresponding to a flow direction ofair passing through the vane assembly, the root portion being adapted tobe mounted to the supporting shroud of the vane assembly, said tiphaving a slot defined therein between said leading and trailing edges ofsaid airfoil, said slot being configured to receive a portion of thesupporting shroud therein for mating therewith, thereby restrictingmovement of said vane tip relative to the supporting shroud in at leastsaid flow direction.

Further details of these and other aspects of the present invention willbe apparent from the detailed description and figures included below.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures depicting aspects ofthe present invention, in which:

FIG. 1 is a side view of a gas turbine engine, in partial cross-section;

FIG. 2 is a side cross-sectional view of a vane assembly according to anembodiment of the present invention;

FIG. 3 is a perspective side view of a vane which is part of theassembly shown in FIG.2;

FIG.4 is a perspective underside view of a grommet which is part of theassembly shown in FIG.2;

FIG. 5 is a perspective side view of a portion of an inner shroud whichis part of the assembly shown in FIG.2;

FIG.6 is a perspective side view of a portion of the assembly shown inFIG.2, showing a mating of the vane, grommet and inner shroud; and

FIG.7 is a perspective side view of an inner shroud and grommet assemblyaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight, generally comprising in serial flowcommunication a fan 12 through which ambient air is propelled, amultistage compressor 14 for pressurizing the air, a combustor 16 inwhich the compressed air is mixed with fuel and ignited for generatingan annular stream of hot combustion gases, and a turbine 18 forextracting energy from the combustion gases.

Referring to the FIG.2, the vane assembly 20 is located downstream ofthe fan 12. The vane assembly 20 includes an inner shroud 26 and aplurality of vanes 22 extending radially between the inner shroud 26 andan engine casing or an outer shroud 21. The inner shroud 26 includes ashroud ring 34 and a shroud web 36. Each of the vanes 22 has an airfoilportion 23 extending between the vane tip 24 and the vane root 25. Thevane root 25 is attached to the outer shroud 21 and the vane tip 24 isretained in a grommet 28 inserted into an opening 54 (see FIG.5) of theshroud ring 34. Throughout this description, the axial, radial andcircumferential directions are defined respectively with respect to thecentral axis, radius and circumference of the shroud ring 34.

As seen in FIGS. 2 and 3, the airfoil portion 23 of each vane 22 definesa leading edge 27 and a trailing edge 29, such that an airflow passingthrough the vane assembly 20 will flow from the leading edge 27 to thetrailing edge 29. The vane tip 24 includes a slot 38 defined therein andlocated between the leading and trailing edges 27, 29. The slot 38 has agenerally rectangular shape and extends radially from the vane tip 24.At the opposite extremity of the vane 22 proximate the vane root 25 isdisposed a button portion 31, which corresponds generally to the shapeof the airfoil portion 23 however is slightly enlarged relative thereto,but nevertheless remains smaller than the adjacent vane root 25. Thebutton portion 31 includes relatively blunt leading and trailing ends.As seen in FIG. 2, the button 31 is received within an outer grommet 33disposed within the outer shroud 21 proximate the root end of the vane22. The blunt vane button 31 accordingly helps to prevent the relativelysharp leading and trailing edges 27 and 29 of the vane airfoil 23 fromtearing the outer grommet 33 during the assembly and/or disassemblyprocess of the vane assembly or in the event of a bird strike.

Referring to FIG.4, each grommet 28 includes a base portion 50 connectedto a lip 46 by a recessed portion 48. The base portion 50 defines twoopposite elongated lateral surfaces 49 extending generally along theaxial direction. Two spaced apart tongues 40 extend perpendicularly fromthe lip 46 along the circumferential direction and define a slit 42therebetween. A cutout 44 corresponding in shape to the vane tip 24 isdefined within the grommet 28, extends through the base and recessedportions 50, 48, and is bordered by the lip 46. The grommet 28 also hasa leading edge 30 and a trailing edge 32 connecting the lateral surfaces49 and corresponding to the leading and trailing edges 27, 29 of theassociated vane 22, as can be seen in FIG.2. The grommets 28 arepreferably made of a flexible material, such as rubber or the like, inorder to be able to dampen vibrations of the assembly.

Referring to FIGS. 2 and 5, the shroud ring 34 has an inner surface 35and an outer surface 37 defining a circumference of the shroud 26. Theshroud web 36 is circular and extends generally radially from the innersurface 35 of the shroud ring 34 around the entire circumferencethereof. The openings 54 are distributed along the circumference of theshroud ring 34. Each opening 54 corresponds in shape to the recessedportion 48 of one of the grommets 28 and is oriented according to adesired orientation of the vane 22 within the airflow. Thus, a grommet28 is receivable within each opening 54, with the base portion 50thereof abutting the outer surface 37 and the lip 46 abutting the innersurface 35. Adjacent to each opening 54, a mating slot 56 is definedwithin the shroud web 36.

Referring to FIGS.2, 4 and 6, each of the openings 54 of the shroud ring34 receives the recessed portion 48 of a grommet 28. The shroud web 36,at the mating slot 56, is received within the slit 42 of the grommet 28,with one of the tongues 40 abutting each side of the web 36. The vanetip 24 is inserted into the grommet cutout 44, the tongues 40 and shroudweb 36 being received within the vane slot 38. Alternately, it is alsopossible to provide a deeper grommet slit 42 and vane slot 38 such as toeliminate the need for the mating slot 56.

Referring to FIGS. 4 and 7, the base portion 50 of each grommet 28 isshaped so that upon installation of the grommets 28, the lateralsurfaces 49 of each grommet 28 will be in close contact with the lateralsurfaces 49 of adjacent grommets 28, such that the base portions 50together form a continuous gas path surface 52 along the entirecircumference and at least an axial portion of the shroud 26. Thisconfiguration eliminates the need to use adhesives or similar measuresto maintain the grommets in position, since the gas flows over thegrommets, “pushing” them radially inward, instead of flowing betweenthem and producing a lifting force thereon. The airflow is also smoothersince it is not perturbed by an uneven surface which would be producedwith conventional grommets having free spaces therebetween.

Alternatively, it is possible to provide an annulus portion or an entireannulus formed by the combined base portions 50 of the grommets 28,which are integrally connected to each other through the lateralsurfaces 49 to form a single unit. In the case of an entire annulus, thegrommets 28 would have to be made of a material sufficiently elastic tobe able to stretch the annulus for insertion of the grommet lips 46 ininto the shroud openings 54.

The vane assembly 20 thus efficiently retains the vane tip in the axialdirection, providing additional stability to the vane position whichreduces the risk of rearward movement of the vane tip 24 upon impact ofa foreign object. This, in turn, reduces the risk of damage to thegrommet 28 and adjacent components upon the impact of the foreignobject. The vane slot 38 and mating slot 56 are easy to machine, and thegrommet 28 with tongues 40 and slit 42 can be manufactured using thesame process as other types of grommets.

The vane assembly 20 eliminates the need for adhesives or the like tomaintain the grommets in place, which reduces costs and simplifiesproduction and maintenance operations.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without department from the scope of the invention disclosed.For example, the vane assembly 20 can be used for other types of enginestators as well as in different fields, such as in ventilation systems.The grommets 28 can be used in outer shrouds as well as other types ofvanes or rotor blades. Still other modifications which fall within thescope of the present invention will be apparent to those skilled in theart, in light of a review of this disclosure, and such modifications areintended to fall within the appended claims.

1. A vane assembly comprising a vane and a grommet engaged therewith,the vane having a root, a tip and an airfoil portion extending betweenthe root and the tip, the root including an outer platform and arecessed portion adjacent thereto and interconnecting the airfoilportion and the platform, the recessed portion protruding beyond aprofile of the airfoil a distance less than the outer platform, and thegrommet having a lip sealingly surrounding said recessed portion of theroot of the vane and a circumferential portion protruding around aperimeter of the lip in engagement with an inner surface of theplatform, the circumferential portion having a profile corresponding tothat of the airfoil portion.
 2. The vane assembly as defined in claim 1,wherein the grommet is made of an elastic material.
 3. The vane assemblyas defined in claim 2, wherein the grommet is stretchable to allow theplatform to pass within a slot defined in the circumferential portionand bordered by the lip.
 4. The vane assembly as defined in claim 2,wherein the lip surrounds the recessed portion of the root of the vanein a stretched state.